We study the structural characteristic of the variable DA white dwarf G117B-15A by applying the methods of asteroseismology .
For such a purpose , we construct white dwarf evolutionary models considering a detailed and up - to - date physical description as well as several processes responsible for the occurrence of element diffusion .
We have considered several thickness for the outermost hydrogen layer , whereas for the inner helium- , carbon- and oxygen-rich layers we considered realistic profiles predicted by calculations of the white dwarf progenitor evolution .
The stellar masses we have analysed cover the mass range of 0.50 \leq { M } _ { * } / M _ { \odot } \leq 0.60 .

The evolution of each of the considered model sequences were followed down to very low effective temperature ; in particular , from 12500K on we computed the dipolar , linear , adiabatic oscillations with radial order k = 1 , \cdots, 4 .
We find that asteroseismological results are not univocal regarding mode identification for the case of G117B-15A .
However , our asteroseismological results are compatible with spectroscopical data only if the observed periods of 215.2 , 271.0 and 304.4 s are due to dipolar modes with k = 2 , 3 , 4 respectively .

Our calculations indicate that the best fit to the observed period pattern of G117B-15A corresponds to a DA white dwarf structure with a stellar mass of 0.525 M _ { \odot } , with a hydrogen mass fraction \log { { ( M _ { H } / M _ { * } ) } } \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ > $ } } } -3.83 at an effective temperature T _ { eff } \approx 11800K .
The value of the stellar mass is consistent with that obtained spectroscopically by Koester & Allard .